Coated optical fibers with small radii are attractive for reducing the size of cables, decreasing cable cost, and efficiently using existing duct infrastructure for cable installations. Reduced-radii fibers typically have the same glass radii as standard optical fibers (125 μm), but use thinner layers as primary and/or secondary coatings. Reduced coating thickness, however, compromises the protective function of the coatings. As a result, much effort in the field has been directed to developing new coating materials that maintain adequate protection at small thicknesses and new glass compositions or index profiles that can tolerate more pronounced bending without compromising signal intensity or quality. Although bend-insensitive coated optical fiber designs with reduced diameters have been proposed in the prior art (see, for example, US Patent Application Pub. No. 20100119202), the nominal mode field diameter (MFD) of these fibers at 1310 nm is typically only ˜8.6-8.8 μm. Such mode field diameters lead to high splicing/connectorization losses upon connection of the reduced-diameter fiber to standard single mode fibers (SMF) (which have a nominal MFD of about 9.2 μm).
To avoid signal losses when connecting low-diameter fibers to existing, standard single mode fibers, it would be desirable to develop an optical fiber having a reduced radius and a mode field diameter that is compatible with that of standard single mode fibers.